1. Field of the Invention
This invention regards an arrangement by a hydraulic jar device, especially for use in underground wells, where the jar device is installed in a pipe string led down into the well, and designed so that e.g. a stuck object in the well may be loosened or broken up by upward or downward percussions from the jar device, where the jar device comprises a casing member, a connector sleeve, a jar, the casing member and connector sleeve each having separate longitudinal through bores, while the jar has a bore such that hydraulic liquid may pass in the jar device, and where the jar device is provided with a piston associated with a valve designed to close and open a bore during the percussion cycle, the piston valve being designed, respectively, to be closed by the inflow of hydraulic liquid and be opened by a tension spring tensioned during the percussion cycle, when the spring force of the tension spring exceeds the pressure from the inflowing hydraulic liquid, to enable the piston to displace the jar relative to the casing member in order to carry out the percussion.
2. Background of the Related Art
Such jar devices are often used in connection with anchoring of valves, measurement equipment and other equipment downhole. The jar device is provided in a pipe string, e.g. a drill pipe string or coiled tubing, and equipment to be placed in the well is fitted to the lower end of the jar device. As mentioned, the jar device is provided with a passage such that inflowing liquid may pass before the jar device is actuated for percussion. The equipment to be placed in the well may be equipped with grippers, spring bosses or something else that will grip e.g. grooves or seating areas in the wall of the well. In order to ensure that the equipment does not come loose, it is often provided with a locking device to be actuated when at least one shear pin is broken off. In those cases where the pipe string is not able to transfer sufficient force to break off at least one shear pin, it may be broken by means of the jar device. Moreover, the jar device is often used purely as a measure, so that the equipment may be loosened, were it to get stuck.
Such hydraulic jar devices are often pre-tensioned by means of an external spring over the jar device. Alternatively, a long drill string or coiled tubing may constitute the spring element. The percussion is carried out by impact areas on the jar device being moved apart, whereupon the pre-tensioned spring sends the impact areas back towards each other. As mentioned, the jar device comprises a hydraulic piston provided with a passage and an associated valve. The valve is normally open, so that liquid may pass through the piston of the jar device when not actuated for percussion. When the jar device is to be actuated for percussion, increasing the flow rate of the inflowing hydraulic liquid closes the passage, so that the valve is closed at the time in question during the percussion cycle. Alternatively, pushing the jar into the casing member may in one embodiment actuate the device. At this, the piston and also the impact areas of the jar device will be displaced relative to each other during the preparation for the percussion. At the same time, the spring is tensioned further as a result of the movement in the jar device. The piston valve is opened when, during the percussion cycle, the jar device has been brought to the extreme position in question, to allow the liquid to flow through the piston again. The hydraulic force against the piston will then suddenly decrease, and the external, associated spring over the jar device will send the impact areas against each other in order to carry out the percussion, whereupon the percussion cycle is repeated.
The use of a spring that can be pre-tensioned from the outside in order to drive the percussion in the jar device is known. It is further known to design the spring so as to allow it to be pre-tensioned either by pulling the pipe string in the direction away from the jar device or pushing the pipe string in the direction towards the jar device. The magnitude of the impact force may be varied through the pre-tensioning of the spring. When the pre-tensioned spring over the jar device is in a neutral position, hydraulic liquid may be passed through the pipe string without actuating the jar device. The jar device is actuated for percussive movement by a pressure increase in the hydraulic liquid contained in the jar device; this will result in cyclic closing and opening of the piston valve, so that the jar device prepares and performs the percussion in the percussion cycle by displacing the relevant components of the jar device, whereupon the procedure is repeated for new percussions. In one embodiment, the jar device may, as mentioned above, be actuated through the jar being pushed into the casing member.
In many of the known jar devices, see e.g. U.S. Pat. Nos. 4,807,709, 3,570,611, 3,379,261 and 3,361,220, the weight of the equipment hanging from the jar device is often sufficient to actuate the piston valve, so as to close the passage for the hydraulic liquid, thereby actuating the percussion effect. This means that it is not possible to circulate liquid through the pipe string when the jar device is being run into or out of the well. If prolonged circulation is required, the percussion effect may damage the equipment. The hydraulic parts of the jar device such as the piston and valve components, will become worn during operation and therefore require regular replacement. Upon lengthy operation requiring circulation of liquid, parts of the jar device may wear significantly before the jar device comes to be used in the required operations. This may result in a reduced percussion effect and faulty operation. However these are conditions that have essentially been remedied by the jar device according to NO patent 304 199. Here, an efficient, reliable and robust hydraulic jar device of the above-mentioned type has been provided through relatively simple and reasonable means. Furthermore, circulation of liquid such as drill fluid through the jar device is possible without this being actuated upon pre-tensioning of the spring, and it is possible to initiate the percussion effect by increasing the pressure of the inflowing volume of liquid, as the piston valve can not close until there is an increase in pressure in the inflowing liquid.
However the known jar devices, especially jar devices with upward percussions, suffer from a shortcoming in that the impact areas in question are provided on the outside of the jar device. Consequently, the percussion effect may be limited by influences from the outside of the jar device, e.g. by contaminants depositing between the impact areas. Another shortcoming of known jar devices is that the hydraulic liquid can close the piston valve before the impact areas has reached full impact against each other during the final period of the percussion cycle. This means that the liquid over such a prematurely closed piston valve will brake the percussion and give a reduced percussion effect.